Renal 2 Main points

Use the following concentration-time data to determine the drug’s elimination rate constant

-k = ln(C2-C1)/(t2-t1)

k = 0.0842 hr-1

Given the following information, calculate the plasma concentration of the drug 3 hours after an IV bolud administration:

• Dose: 100mg

• V = 45L

• k = 0.116hr-1

• C₀ = Dose/V

  • = 100mg/45L

  • = 2.22mg/L

• C_t = C₀(e^-kt)

  • = 2.22mg/L(e^{-0.116hr-1(3hrs)})

  • = 2.22mg/L(0.7061)

  • = 1.568 mg/L = 1.6mg/L

For a drug with the following characteristsics, what woul dbe the concentration after you infused the drug for 8 hours? What about 16 hours after stopping the infusion?:

• R = 7.7mg/hr

• V = 450L

• k = 0.066hr-1

• After infusing the drug for 8 hours

  • CL = V(K)

    • = 450L(0.066hr-1)

    • = 29.7L/hr

  • Css = R/CL (R= rate → dose/tau)

    • = 7.7mg/hr/(29.7L/hr)

    • = 0.259mg/L

  • C_t = Css(1-e^-kt)

    • = 0.259mg/L(1-e^{-0.066hrs-1(8hrs)})

    • = 0.11mg/L at 8 hours of infusing

• 16 hours after stopping the infusion

  • C_{afterstopping} = C_whenstopped(e^{-kt_{afterstopping}})

  • C_{16 hours after stopping} = 0.11mg/L(e^{-0.066(16 hours after stopping)})

    • = 0.0383mg/L 16 hours after infusion was stopped

For a drug with the following characteristics, what is the ratio of Cmax,ss to Cmax,single dose:

• Dose = 250mg

• Tau = 6 hours

• V = 15L

• k = 0.15hr-1

• Cmax,ss = Cmax,single dose (AR)

  • AR = Cmax,ss/Cmax,single dose

• AR = 1/(1-e^-k(tau))

  • =1/(1-e^{-0.15hrs-1(6)})

  • = 1.69

What are the administration and monitoring parameters/goals for K and Mg IV dosing? What happens if a patient has both low K and Mg (what changes)?

Mg 2g IVPB first, then K 80mEq IVPB + ECG monitoring

• If K is less than 3.5 mEq/L we can consider IV potassium.

  • 10 mEq K corresponds to a 0.1 mEq/L increase in K

    • In patients with eGFR >45mL/min

  • ECG monitoring should be used if the infusion rate is >10mEq/hr (patient also has history of afib)

• If Mg is less than 1.6 mEq/LWhat we can consider IV magnesium.

  • 1 g Mg corresponds to a 0.1 mEq/L increase in Mg

    • In patients with eGFR >45mL/min

• MG should be administered first since the nephron contains magnesium-gated potassium channels (ROMK) → administration of magnesium first will help to prevent additional potassium loss through this channel.

What is the equation to use for Na deficit to bring back to a goal level?

Na Deficit: 0.6 𝐿/𝑘𝑔 ∗ 𝑊𝑡 ∗ (𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝑁𝑎 − 𝑠𝑒𝑟𝑢𝑚 𝑁a)

What is the equation to use for free water deficit to bring back to a goal level?

0.6 𝐿 𝑘𝑔 ∗ 𝑊𝑡 ∗ (𝑠𝑒𝑟𝑢𝑚 𝑁𝑎 / 𝑔𝑜𝑎𝑙 𝑁𝑎 − 1)

What units is infusion rate?

mL/hr